The present invention relates generally to remote copy in storage systems and, more particularly, to methods and apparatus for low traffic failback remote copy.
The remote copy function in a storage system supports synchronous or asynchronous I/O replication between volumes of local and remote storage subsystems. Asynchronous remote copy function can maintain the consistency of I/O order. When a shutdown or some other failure occurs at the local storage subsystem, the remote storage subsystem takes over the data in a failover process. During failover, the remote storage subsystem will be accessed to continue processing data. After the local storage is repaired, the local storage is restored using data from the remote storage subsystem in a failback process. By recording the accessed area during the period from failover to failback, the storage system can perform a delta copy instead of a full copy, thereby decreasing the traffic for failback.
The delta copy, however, requires that the local storage subsystem continue to be active after failback and not lose data. When the local storage subsystem loses data or when it needs to restore to another storage subsystem, the data in the remote storage subsystem has to be copied entirely. This causes a data traffic increase.